Part of Hall of the Universe.
AMNH/D. Finnin 0.8 to 8 Times the Sun’s Mass
Stars of intermediate mass have lifetimes that range between 50 million and 20 billion years. Nuclear reactions in these stars make most of the carbon and nitrogen in the universe. When intermediate-mass stars die, they blow off their atmospheres, dispersing such elements across space.
Old Age: Red Giant
After depleting the hydrogen in its core, an intermediate-mass star contracts and heats up until it sets off the fusion of helium into heavier elements. Helium fusion provides a second stable phase, covering the last 10 percent of the star’s life. The increase in energy production puffs out the star’s atmosphere, resulting in a highly luminous red giant star. When the Sun reaches this stage, it will engulf the orbit of Venus and evaporate Earth’s oceans.